Due to manufacturing needs, mobile phone manufacturers use mechanical structure where the antenna circuit (i.e. the physical antenna and its matching and filtering circuits) is connected to the phone handset with spring contacts, instead of soldering for instance.
Badly connected antenna spring contact may cause a situation where the phone works somehow in locations where the mobile network's coverage is strong (big cities, etc.) and poorly in the country side or in any locations where the network's coverage is low (lower signal strength).
This situation is very hard to detect even by the end user. Plus, even in the case where the end user detects a bad behavior of his or her mobile phone handset, s/he will bring it to a service center where usually the network coverage is strong. The service center clerk will then not be able to notice any problems with the mobile phone (unless the antenna circuit is completely disconnected).
There is therefore a need for automatic testing mechanisms, usually referred to as Built-In Self Test (BIST) techniques or production tests.
Various production test and BIST techniques have been developed to test the antenna circuit presence in microelectronic transceivers. Generally speaking, they all fall in one of the following categories.
A first prior art category consists in measuring the impedance of the antenna circuit. Using a peak detector that is integrated in the power amplifier block of the transmitter, the peak voltage of the transmitted signal is measured on-chip. By measuring this peak voltage, the load impedance at the antenna circuit connection pads can be calculated and compared with a predetermined range of admissible values so as to check whether the antenna circuit is present (well soldered) or not.
A second prior art category consists in measuring the output power of the transmitter. The device is programmed to radiate at a known power and then a spectrum analyzer measures the really outputted power (taking into account antenna-to-antenna loss over the air). By comparing these 2 values, a connection default of the antenna circuit can be detected. This technique requires extra equipment like a spectral analyzer and its associated antenna, and is therefore more devoted to production test than to BIST.
A third prior art category consists in measuring the signal, or the signal to noise ratio (SNR) of the receiver. A continuous wave signal is radiated to the antenna of the receiver and the resulting signal level and frequency offset are measured using an on-chip DFT in the receiver circuit. A measured input power below the transmitted value, or a measured frequency offset higher than a predetermined one means that the antenna circuit is not well connected. This approach requires extra equipment like an RF signal generator and its associated antenna. Like the previous one, it is therefore more devoted to production test than to BIST.
A fourth category of prior art consists in performing a receiver/transmitter loopback test. This technique is for instance used in TM transceiver. The transmitter output a frequency modulated single tone carrier (for example, set at 87.5 MHz). The antenna voltage is fed through a matched attenuator to the internal LNA input. At the output of the LNA, the signal strength is measured by a level detector. The measured value is then compared to a lower limit. In case the measured value is above the limit, the antenna circuit is considered to be ok. If the measure value is below the lower limit, then the antenna circuit is considered as being in default. This mechanism is based on the fact that when a bad quality factor caused by the absence of the antenna circuit attenuates the transmitted signal level, the received signal strength has a lower value.
However, these solutions are insufficient in detecting a defective antenna mechanical contact. One of the reasons is that unlike traditional defective soldered contacts, a defective antenna's mechanical contact (e.g. spring contact) does usually not change substantially the impedance. Notice that mechanical contacts is the general case, spring contacts is an example of a widely spread way of doing mechanical contacts.
There is a need for a solution permitting to detect automatically connection defaults of non-soldered antenna circuits, e.g. antenna circuits connected with spring contacts.